The invention relates to a device for monitoring threads on a textile machine by producing a control signal both in the case of an irregularity in the thread and when crossed by a monitoring needle, which is positioned in a housing under spring tension in close proximity to a light-emitting and receiving device in the thread's plane and in the pivotal region of the needle. Such devices are for example mounted on the bobbin creel of a warp system, in order to monitor the presence of threads drawn from the bobbins. If a thread breaks, the winding apparatus is automatically stopped.
A comparable device of this kind is known of example from DE-C-29 15 749 of the Applicant. In this case the control signal is triggered by the closing of electric contacts when the monitoring needle is pivoted. According to another principle, the control signal is triggered when the pivoting monitoring needle interrupts a light beam directed at a photocell. A thread monitor of this kind is known for example from CH-A-417 491 or from U.S. Pat. No. 4,100,425. Most known thread monitors are additionally provided with a device for locking the monitor needle in the operating position so that, in a row of adjacent monitor needles, individual needles can remain unoccupied without triggering a signal.
In many textile machines, in addition to checking the actual presence of the thread, quality control of the individual threads also has to be carried out. To this ends, a group of threads gathered together in one plane is guided through a light beam. If a yarn imperfection, e.g. in the form of a knot or a thread end passes through the light beam, the quantity of light transmitted decreases, whereby according to the sensitivity setting, a control signal for stopping the machine may also be triggered. A comparable principle is known for example from CH-A-553 270. This quality control of the thread is conventionally carried out immediately before the winding drum, as the threads have to be gathered together there in any case.
A disadvantage of the known devices is that the presence monitoring on the one hand and quality control on the other hand have to be executed in different components and at different places. This considerably increases expenditure on equipment and the possibilities of an operating fault. Furthermore, it is necessary to wind the thread round and through so many guides that threading takes up a relatively large amount of time. The large additional diversions of the thread, e.g. for gathering together and re-separating of the threads, furthermore increase the risk of thread breakages. It is therefore an object of the invention to improve a device of the kind cited at the beginning in such a manner that not only presence monitoring but also quality control of the thread can be carried out in a single unit. This object is achieved according to the invention with a device having the features of claim 1.